It might be all-natural, but that joint you're smoking has a serious carbon footprint: marijuana growth uses 1% of all U.S. energy.

Buzzkill, stoner pals. Your weed is really bad for the environment. Only the stuff that's grown inside, to be fair—the kind of boutique-y, mind-blowing pot preferred by many marijuana dispensaries. It's responsible for 1% of all electricity use in the U.S. That's a $5 billion yearly energy bill—two million U.S. homes' worth—just to get you super stoned.

The sobering news comes from a report by Evan Mills, a longtime energy analyst at Lawrence Berkeley National Labs who, uh, has a friend who told him about all this weed stuff. According to Mills, the problem can be traced back to the high-intensity lighting, dehumidification, air-conditioning, irrigation systems, space-heating, and ventilation systems that all go into making sure marijuana plants grow up to be healthy, smokeable adults. And since the industry operates in the shadows, it hasn't felt the consumer pressure to go green (rimshot!).

Mills's report gets even more intense when the energy consumption figures are broken down into consumer-friendly numbers. Smoking a single joint is the same as leaving a 100-watt light bulb on for 17 hours. For you more committed drug peddlers out there, each kilo is the same as five cross-country drives in a 44-mpg car.

So, smoking a joint of indoor-grown pot is like leaving the lights on for a day, and sitting around for hours with a handful of friends and a bong is as bad carbon emissions-wise as taking a really long road trip. Evan Mills has yet to calculate the added environmental costs of your vaporizer.

The simple solution to this is to nix indoor growing operations; the energy consumption of outdoor operations is virtually nil. But the medical marijuana market is set to grow to $8.9 billion in the next five years, so cutting back is probably out of the question. Instead, marijuana production needs to be legalized, so people will actually cast a critical eye on its energy usage. All the industry has to do is follow in the footsteps of the commercial agricultural industry, which has made strides in energy efficiency in recent years. Then, at least, stoners will have one less thing to be paranoid about. In the meantime, maybe those dispensaries should start selling carbon offsets with your eighth.

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